1. Field of the Invention
The present invention relates to semiconductor processing, and more particularly, to a method for integrating metal-containing films formed in a chemical vapor deposition process into semiconductor devices.
2. Description of the Related Art
In the semiconductor industry, the minimum feature sizes of microelectronic devices are approaching the deep sub-micron regime to meet the demand for faster, lower power microprocessors and digital circuits. The downscaling of complimentary metal oxide semiconductor (CMOS) devices imposes scaling constraints on the gate dielectric material. To increase device reliability and reduce electron leakage from the gate electrode to the transistor channel, semiconductor transistor technology is using high dielectric constant (high-k) materials that allow increased physical thickness of the gate dielectric while maintaining an equivalent gate oxide thickness (EOT) of less than about 10 angstrom.
High-k materials feature a dielectric constant greater than that of SiO2 (k˜3.9). High-k materials can include metallic oxides, oxynitrides, silicon oxynitrides, and silicates, for example Ta2O5 (k˜26), TiO2 (k˜80), ZrO2 (k˜25), Al2O3 (k˜9), HfSiO, HfSiON, HfO2 (k˜25)). Integration of high-k materials into gate stack applications can require an ultra-thin interface layer at the surface of the Si substrate to preserve interface state characteristics and form an interface with good electrical properties. However, the presence of an interface layer lowers the overall dielectric constant of the gate stack and, therefore, the interface layer may need to be thin. The quality of the interface layer can affect device performance, as the layer is intimately connected to the channel of the transistor.
Tungsten (W) and tungsten-containing films are potential gate electrodes in gate stacks. W films can be formed by a tungsten-containing precursor in a chemical vapor deposition (CVD) process. Material properties of W films that are deposited from metal-containing precursors may be poor due to incorporation of contaminants into the W films from reaction byproducts and gas phase contaminants during or following the deposition process. Integration of a W film into a gate stack involves contacting the W film with films of other materials which requires the W film to have good surface morphology and low contaminant levels to prevent diffusion of the contaminants into the other materials. For example, outdiffusion of oxygen contaminants from W films is considered to contribute to increased EOT and flatband voltage shifts in gate stacks.
Therefore, new methods are needed for depositing and integrating tungsten-containing films and other metal-containing films with low contaminant levels into semiconductor devices.